A summary of the effectiveness of an intervention in an outcome domain, based on the quality of research, the statistical significance of findings, the magnitude of findings, and the consistency of findings across studies.
Positive: strong evidence that intervention had a positive effect on outcomes.
Potentially Positive: evidence that intervention had a positive effect on outcomes with no overriding contrary evidence.
Mixed: evidence that intervention’s effect on outcomes is inconsistent.
No Discernible: no evidence that intervention had an effect on outcomes.
Potentially Negative: evidence that intervention had a negative effect on outcomes with no overriding contrary evidence.
Negative: strong evidence that intervention had a negative effect on outcomes.
For more, please see the WWC Glossary entry for rating of effectiveness.
An indicator of the size of the effect from using the intervention. It is the expected change in percentile rank for an average comparison group student if the student had received the intervention, ranging from -50 to +50. At the domain level, the improvement index is only shown if the effectiveness rating is positive, potentially positive, potentially negative, or negative; dashes are displayed for mixed or no discernible effects. At the study level, the improvement index is only shown if the findings are characterized as statistically significant or substantively important (greater than +10 or less than -10); dashes are displayed for an indeterminate effect.
For more, please see the WWC Glossary entry for improvement index.
The percent of each characteristic is based on the sample size of all studies meeting standards that reported data on the characteristic.
Percentages below may not add to 100 percent.
Last Updated: December 2016
This intervention report was prepared for the WWC by Mathematica Policy Research under contract ED-IES-13-C-0010.